Thermodynamic Studies On The Physical And Chemical Characteristics Of Ore-bearing Fluids Of Dashuigou Tellurium Deposit Of Shimian In Sichuan Province

The Dashuigou tellurium deposit is located in northern lower end of Dashuigou dome between Bindong ductile shear zone and Xiyoufang ductile shear zone in Shimian of Sichuan province. The geology structure is very complicated here. The ductile-brittle shear zone and the dome provided advantaged spatial condition for the mineralization and controlled the occurrence of ore bodies. The host rocks for the mineralization are of Triassic metabasic volcano rock and dynamothermal metamorphic marble, greenschist and phyllite. Wall-rock alterations are extensively developed there and the main alterations are carbonatization and silicification. The main minerals are tsumoite, tetradymite, and so on.Based on large geological investigations in the flied and a lot of analytical data gained in the laboratory, the author is studying on the fluid inclusion characteristics of the deposit. This study covers regional geology, ore deposit geology and the fluid inclusions chemistry. The regional geologic settings is studied by applying the modern thoughts and basic methods of architectonices and tectonic-geochemistry. The ore deposit, Te-mineralization, ore bodies, hydrothermal alteration, mineral paragenesis and so on are researched by applying the modern thoughts and basic methods of metallogeny, geochemistry, mineral geology. The fluid inclusions chemistry is based on temperature test by homogenization method on the hot and cold stages for upright Microscopes and on calculating by the geochemical thermodynamics method. As a result, the author calculated the physical and chemical parameters of the ore-forming fluids.As a result, the following conclusions are derived: 1. the tellurium deposit is formed in the site where the plates splice of which is conducive deep fractures systems develop, grant plenary spaces for ore-forming and for ore-bearing fluids activities.2. Within the deposit, the hydrothemal activity is very strong, and the wall rocks are well developed. The mineralization of tellurium is very closely related to the wall rocks alteration. The most important alteration types are dolomitization and silicification. All evidences suggest that the enrichment of tellurium has a very close relationship to the dolomitization. Further more, the alterations of wall rocks have obvious features of zonation and symmetry. These evidences indicate that the tellurium mineralization is formed under the conditions of long-term hydrothermal activity and full reactions.3. The researches of the compositions and features of fluid inclusions and the studies of isotopic geochemistry have shown that the ore-bearing fluids are sources from the deep magmatic hydrothermal fluids with characteristics of high temperature, full of alkali, high ?o2 (free oxygen) and high ?s2 (free sulfur).4. The formation process of the tellurium deposit is the result of the changes of the physical and chemical conditions of hydrothermal systems when the ore-bearing fluids are forced into the forming favorable environment by the deep geological forces. the values of T, P, pH, ?o2 and ?s2 gradually decreased and the the Eh value increased leading the Te and its complexes to be resolved, so that mineraliztion is occured. During the process, Te is enriched by precipitating from the ore-bearing fluids, and formed the deposit.